Defect-modulated structures in Al–Ni–Rh crystalline approximants

Abstract

Defect-modulated Al–Ni–Rh crystalline approximants, which are structurally related to a decagonal quasicrystal with 1.6 nm periodicity, have been found to form in an as-solidified Al₇₅Ni₁₅Rh₁₀ alloy. Their structural features were studied by a combination of high-resolution electron microscopy (HREM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The results show that the prefect structures of Al–Ni–Rh crystalline approximants are characterized by periodic arrangements of hexogen units (H) constructed from atom columnar clusters. Defect-modulated structures were formed due to ordered arrangement of one- or two-dimensional structural defects of high density. The basic structural defect is associated with incorrect arrangements of atom columnar clusters which appear as polygons different from the H units. These polygons of atom columnar clusters represent a type of linear defect extending along the columnar axis direction, and they can array to form a planar defect. By means of the HAADF-STEM imaging technique, the structural nature of the core area for the linear defect, which usually exhibits dark contrast in HREM observations, has been clearly revealed.

Acknowledgements

This work was supported in part by 973 National Research Project and by the Academic Research Fund from Beijing Municipal Commission of Education.